Variable ratio steering gear



March 1l, 1947. 1 M p GRAHAM 2,417,072

` VARIABLE RATIO STEERING GEAR Filed April 18, 1945 2 Sheets-Sheet l yy/wml@ March 11', 1947. M, P, GRAHAM vARIABLE'RATIosTEERING GEAR 2 Sheets-Sheet 2 Filed April 18, `1945 ""IIIIIIIIII" Patented Mar. 11, 1947 VARIABLE .RATIO STEERING GEAR Matthew P. Graham, Detroit, Mich., assigner to Thompson Products, Inc., Cleveland, Ohio, a.

`corporation of Ohio Application April 18, 1945, "Serial No. 583,945

sciame. (o1. 'r4-iss) This invention relates 4to steering Amechanisms of the type disclosed and claimedin-theYJ-ames H. Booth application entitled: Variableoatio steer ing assembly, 4Serial No. 589,039, filed of even dateherewith.

Specifically this invention deals with an improved means for adjusting rotating movements of -a slidable member Ato `vary the reductionl ratio ina steering assembly or the like.

In the above referred to Booth application, Serial No. 589,039, there 'is vdisclosed and claimed a steering assembly wherein a vslidable pitrnan arm shaft is rotated :to swing the pit-nien arm in amounts controlled by a link having an adjustable pivot anchor. In order that Athis anchor could be shifted without `driving the pitman arm, it was necessary toprovide an arcuate travel path for the anchor having a radius centered on the pivot for the other end of Lthe link when vthe dirigible wheels were in straight-ahead position. The necessity for such an arcuate travel path for the link anchor has been eliminated by the present invention whereby a rotatable vcam plate is provided for vthe slidable pitman arm shaft. This cam plate kis easily shifted to vary Ithe degree of swinging -of the pitman arm relative to shifting movement of the pitman Iarm shaft.

It is, therefore, an objectief the Apresent invention to provide an improved steering assembly wherein 'the driving reduction can be varied at will by' shifting an easily actuated :cam member.

A. still further object ofthe invention is toprou vide a .steering assembly for `dirigible parts wherein an actuating part effects sliding movement `of a pitman armlshaft and'whereinian adjustable cam controls swinging 'of the pitman arm in response to shifting of the shaft.

Another `object of the invention is to provide an improved steering mechanism for automotive vehicles whereinthe reduction ratio between `driv ing and driven parts is .readily varied :by simple manipulation of :a `rotatable member.

Another objectof the invention is to provide a variable driving ratio steering assembly embody ing la cam plate for resolving shifting `movement of a pitman arm shaft into rotating movement in amounts that can be varied at will by the operator.

Other and further objects of the invention will be apparent to those skilled in the art by the following detailed description of the :annexed sheets of .drawings which, by way of preferred example, illustrate one embodiment of the invention.

kOn `the drawings:

Figure 1 is airagmentary top plan View of an automobile chassis having independently suspended dirigible wheels actuated by a steering assembly according to thisinvention.

Figure 2'svertical cross-sectional view taken along the Iline Iii-*II of Figure l.

Figure 3 is. an enlarged vertical cross-sectional View, with ,parts inV elevation, taken along the line III-III of Figure l.

Figure 4 is an enlarged. front end elevational viewtaken along the line IV-IV of Figure 2.

.Figure 5 is. enlarged top plan view of the device shown in Figure 4, with parts broken away and shown in horizontal cross section.

Figure 6 is a diagrammatic plan View illustrating actuation of the cam device.

As shown on the-drawings:

In Figures 1 and 2 the reference numeral if! designates generally the chassis of an automotive vehicle. The chassis iii hasside frame beams it, I l and a cross beam l?? near the front end thereof. Links or sub-axles i3, l5 are pivotally mountedon the cross beam l2 for supporting dirigible wheels til, itl in `independent relation `relative to the chassis. Spindle assemblies i5, l5 carry the wheels lil, it on the links or sub-axles i3, I3. These spindle assemblies E5 have Steering arms ld, Elia. projecting rearwardly therefrom and connected to tie .rods it, it? which, in turn, are connected to a center steering arm il pivoted on the cross beam i2 as at lil.

.A `drag link lil connects the center steering l? with a pitrnan arm Ztl on a slidable pitman arm shaft il projecting from a gear box 22 which is mounted on a side frame beam ii. The gear box Eil has an .integral late-rally extending .arm 23 and aforwardly eXtending arm 2.

.A bell crank member 25 is pivoted to the end of the arm 23 at Z6. A link El is connected to one arm of the bell crank by means of a ball. stud 2t. The other arm of the bell crank 25 has a ball stud 2.9 thereon connected to a control rod 3i?. This control rod can extend through the dash (not shown) .of the vehicle iii to be conveniently accessible :to the operator for shifting the bell crank EB aboutits pivot 255,

The arm 2li rotatably supports a cam member 3l on anti-friction bearings VB. The cam mein-Y ber 3:5 has an arcuate slot t2 therein receiving the ball endo!" a ball. on the boss 2305 of pitman arm This boss 2cd of the pitman arm is secured on the slidably mounted pitman arm shaft 2 l.

The cam .member 3l has a ball st d 34 thereon seated in theendof thelinlcl. l

As shown in Figure 5, the gear box 22 has bearing sleeves 35 slidably supporting the pitman arm shaft 2|. The pitman arm shaft 2| projects forwardly from the bearing box 22 and a flexible boot 36 is connected at one end to the projecting portion of the shaft and at the other end to a boss 31 of the bearing box which boss supports the front bearing sleeve 35.

A collar 38 is formed integrally on, or is integrally affixed to the shaft 2| in the bearing box 22. A bearing 39 surrounds the shaft 2| and abuts the collar 33. A washer 40 surrounds the bearing 39 and a nut 4| is threaded on the shaft 2| to thrust against the washer 4i). A worm follower 42 is rotatably carried on the bearing 33 between the washer 40 and the collar 38. The follower 42 can thus rotate freely around the shaft 2| but is held against relative longitudinal movement on the shaft by the collar 38 and the washer 4i).

A cage 43 is carried in the gear box 22. This cage is mounted eccentrically and has a flange 43a with a slot therein receiving 'a lock screw 44 which is threaded into the gear box. The cage 43 carries roller bearings 45. A worm 46 is rotatably supported by the roller bearings 45. This worm is mounted on a steering shaft 4l projecting from the gear box. A collar or sleeve 48 is threaded into the cage 43 to thrust against one of the bearings 45 for holding the assembly in position.

The worm 46 meshes with the follower 42 and the eccentric cage 43 can be adjustably rotated in the gear box 22 to obtain proper meshing engagement between the worm and worm follower. This arrangement provides adjustment for wear take- Rotation of the steering shaft 4l drives the worm 46 to drive the follower 42 for sliding the pitman arm shaft 2| into and out of the gear box 22. The shaft 2| carries the pitman arm 20 therewith.

Since the pitman arm boss Za has the ball stud 33 thereon seated in the groove 32 of the cam plate 3|, sliding movement of the pitman arm shaft 2| is resolved into rotating movement for swinging the pitman arm 20 to actuate the drag link i9. This drag link i9 propels the center steering arm Il' about its pivot I8 to move the tie rods |3 for actuating the steering arms |5a about their pivots thereby swinging the dirigible wheels I4, i4.

The amount of rotative movement of the shaft 2| resulting in swinging movement of the pitman arm 20 depends upon the setting for the cam plate 3| since, as shown in Figure 6, the arcuate groove 32 in this cam plate can be rotated for creating different amounts of swinging movements of the pitman arm relative to the amounts of slidable movement of the pitman arm shaft 2|.

Thus, when the steering shaft 41 is actuated by the driver of the vehicle I0, the worm 46 drives the follower 42 to slide the pitman arm shaft 2|. This pitman arm shaft 2l, in moving toward and away from the gear box 22, will carry 'the pitman arm 2|) therewith. However, the path of movement of the pitman arm 20 will be controlled by the cam slot 32 of the cam plate 3|. Since this cam slot 32 is arcuate, the pitman arm 2B will be swung in an arc determined by the cam slot. As shown in Figure 6, since the cam plate 3| can be rotated, the cam slot 32 can assume different positions and therefore the amount of swinging of the pitman arm' 20 relative to the amount of sliding movement of the pitman arm shaft 2| can be varied. 'I'his variation is controlled by the link 2'|, which rotates the cam plate 3l, for example, to swing the slot 32 between solid and dotted line positions shown in Figure 6. 'I'he link rod 21 is actuated by the bell crank 25 which bell crank, in turn, is moved by the control link 30.

It is thus evident that the swinging movement of the pitman arm 2li to actuate the center steering arm |1 is controlled relative to the sliding movement of the pitman arm shaft 2| by the setting of the cam plate 3|. In this manner, the driving reduction of the steering assembly is varied as desired without change of gears or operating parts. It is thus possible, according to this invention, to vary the reduction in the steering linkage without substitution of parts, and to provide for comfortable steering under all conditions encountered in driving an automotive vehicle. For example, a low driving reduction can be utilized for driving at ordinary driving speeds, and a high driving reduction can be utilized for parking the vehicle.

It will, of course, be understood that various details of construction may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

1. In asteering assembly including a driving worm, a follower driven thereby, a slidable shaft rotatably supporting said follower, and a pitman arm on said slidable shaft, the improvement of a rotatable cam plate having an arcuate cam slot, means on said pitman arm riding in said cam slot, and manually operative means for rotating said cam plate to vary the position of said cam slot for regulating the swinging movement of the pitman arm relative to the sliding movement of said slidable pitman arm shaft.

2. In a steering assembly including a slidable pitman arm shaft, a pitman arm actuated thereby, and a steering linkage actuated by said pitman arm, the improvement of a cam member operatively connected to said slidable pitman arm shaft for resolving sliding movement thereof into swinging movement of the pitman arm, and means for adjusting said cam member to vary the amount of swinging movement relative' to the amount of sliding movement.

3. A steering assembly comprising a gear box, a worm rotatably mounted in said gear box, a pitman arm shaft slidably mounted in said gear box, a follower freely rotatable on said pitman arm shaft and meshed with said worm. an arm projecting laterally from said gear box, a bell crank on said arm, a link actuated by said bell crank, a control rod for swinging said bell crank, a second arm projecting from said gear box, a cam plate rotatably mounted in said second arm, means connecting said link to said cam plate for rotating the cam plate in response to movement of said bell crank, said cam plate having a cam groove therein, a pitman arm on said slidable shaft, and means on said pitman arm seated in said cam groove for resolving sliding movement of the pitman arm shaft into swinging movement of the pitman arm in accordance with the setting of the cam plate.

4. In a selective mechanical movement assembly including a driving part, a sliding part driven thereby, and a swingable member on said sliding part, the improvement of a rotatable cam plate engaging said swingable member for resolving sliding movement ofthe sliding part into swinging movement for the swingable member, and means for rotating said cam plate to vary the amount of said swinging movement relative to the amount of said sliding movement.

5. A steering assembly comprising a gear box, a worm rotatably mounted in said gear box, a steering shaft for driving said Worm, a pitman arm shaft slidably mounted in said gear box, a follower rotatably mounted on said pitman arm shaft in meshed engagement with said worm,

a pitman arm on said pitman arm shaft, a rstf arm on said gear box, a rotatable cam plate carried by said rst arm, an arcuate cam slot in said cam plate, means on said pitman arm riding in said cam slot, a second arm projecting from said gear box, a bell crank on said sec` ond arm, a link connecting said bell crank with said rotatable cam plate, and means for swinging said bell crank on said second arm for rotat` ing the cam plate to vary the position of the cam slot for varying the amount of swinging movement of the pitman arm relative to the amount of sliding movement of the pitman arm shaft.

6. A variable ratio mechanical movement assembly comprising a rotatable driving part, a reciprocal driven part, and an adjustable cam coacting with said driven part to resolve the driven reciprocal movement thereof into rotating movement whereby the setting of the cam will determine the ratio of rotating movement between the driving and driven parts.

MATTHEW P. GRAHAM.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Number Country Date 789,745 French Aug. 26, 1935 480,054 British Feb. 16, 1938 

